The NIST calibration service that provides electric energy traceability for the U.S. utility industry is described. Electronic watthour meters, submitted for test, are measured using the NIST Power Bridge, in which complex ac power is defined in terms of the more basic units of voltage, resistance, and capacitance. By integrating power over a known time period, the unit of energy is defined. Calibrations are performed using a synthetic loading technique at power levels between 0 and 60 kW. The basic uncertainty of the NIST Power Bridge is about 15 ppm at 120 V, 5 A, 0 to 1.0 power factor, at 60 Hz. However, calibration uncertainties depend on the power level and the instrument type. Typical uncertainties (k=2) are between 50 and 500 parts per million. A Measurement Assurance Program for 60 Hz energy is also available.
展开▼
